An element with the attribute “tabindex” must not appear as a descendant of the “button” element.

The button role is used to make an element appear as a button control to a screen reader and can be applied to otherwise non-interactive elements like <div>. If you’re already using an <input> element whose type is submit, then it’s redundant to apply it the role button, as that’s implicit.

<!-- Instead of this -->

<input type="submit" role="button">Buy</button>

<!-- Do this -->

<input type="submit">Buy</button>

In HTML, the <button> element is used to create interactive buttons. The W3C HTML Validator message suggests that your <button> element might be missing certain attributes that are typically expected for accessibility or functionality.

Understanding the Required Attributes

1. type Attribute:

   • The type attribute specifies the behavior of the button. It can take one of the following values:
     • submit: Submits the form data to the server.
     • reset: Resets the form data to its initial values.
     • button: A generic button with no default behavior.
   • If omitted, the default value is submit when the button is within a form.

   <button type="button">Click me</button>

2. role and aria-checked Attributes:

   • These attributes are related to ARIA (Accessible Rich Internet Applications) roles and states, which enhance accessibility by providing semantic meaning to assistive technologies.
   • The role attribute defines the type of widget the button is supposed to represent, for example, role="switch" or role="checkbox".
   • If using role="checkbox" or role="switch", the aria-checked attribute indicates whether the button is checked (true), unchecked (false), or if its state is indeterminate (mixed).

   <!-- Example for a button acting as a checkbox -->
   
   
   <button type="button" role="checkbox" aria-checked="false">Toggle Option</button>

Recommendations

• Always define the type attribute to clearly specify the button’s intended behavior, especially within forms.
• If the button acts like a toggle control such as a checkbox or switch, include the appropriate role and use aria-checked to reflect its current state.
• Ensure alignment of ARIA attributes with the intended behavior and visual representation of the button for users, both with and without assistive technologies.

The <summary> HTML element specifies a clickable summary, caption, or legend for a <details> element’s disclosure box. As the <summary> element has an implicit button role, it’s not needed to include it explicitly.

Here’s an example, clicking the <summary> element toggles the state of the parent <details> element open and closed.

<details>
    <summary>I have keys but no doors. I have space but no room. You can enter but can’t leave. What am I?</summary>
    A keyboard.
</details>

A button element, or an element with the role=button attribute, is not allowed to be nested inside an <a> element.

The aria-expanded attribute can only be true, false, or undefined.

This attribute indicates whether a grouping element is expanded or collapsed.